GB2149473A

GB2149473A - Actuator system

Info

Publication number: GB2149473A
Application number: GB08329799A
Authority: GB
Inventors: John Richard Simmons
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1983-11-08
Filing date: 1983-11-08
Publication date: 1985-06-12
Also published as: GB2149473B

Abstract

The system comprises a first linear actuator unit 11 and a second linear actuator unit 10 connected in tandem. The unit 11 is caused to oscillate at a desired relatively high frequency and the midpoint of its oscillation is moved cyclically at a higher amplitude and lower frequency than that of the oscillation. The unit 10 is controlled to provide a cyclic output which opposes the cyclic movement of the unit 11. Additionally the unit 10 may be operated to provide a desired mean operating position for the output oscillations of the system as a whole. The cyclic output movement of the unit 11 prevents wear thereon arising from the aforesaid high frequency operation. The system is applied to the pitch control mechanism of a helicopter rotor to reduce rotor vibration which would be transmitted to the body of the helicopter. <IMAGE>

Description

SPECIFICATION Actuator system This invention relates to an actuator system which can provide a reciprocating output, which output may be used either to impart oscillation to an object, or to oppose transmission of oscillation from an object to a relatively fixed part. In particular the invention is concerned with an actuator system which may be used to effect higher harmonic pitch control of helicopter blades, to reduce vibration levels which would otherwise be transmitted from the blades to a body of the helicopter.

The reciprocating output of such an actuator system may be expected to have a relatively high frequency andsmall magnitude, typical values being 27 Hz and 1 mm. It is anticipated that sustained operation of piston and cylinder unit at the foregoing frequency and magnitude will result in considerable local wear on the piston and the cylinder, as well as on the sealing elements in the unit. The present invention provides an arrangement by means of which the aforesaid local wear may be reduced.

According to the invention there is provided an actuator system comprising first and second actuator units connected in tandem, means for causing said first actuator unit to provide an output which comprises a first oscillatory movement of a predetermined frequency and amplitude and a second oscillatory movement superimposed on said first movement, the frequency and amplitude of said second movement being respectively higher and less than those of said first movement, and means for causing said second unit to provide a third oscillatory movement whose frequency and amplitude are substantially equal to those of said first movement, said third movement being opposite in sense to said first movement.

Embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings in which: Figure 1 shows, diagrammatically, an actuator system according to the invention.

Figure 2 is a section of a piston and cylinder unit forming part of the system of Figure 1, and Figure 3 is a diagram of a system according to the invention as applied to control of the blades of a helicopter.

As shown in Figure 1 two piston and cylinder units 10, 11 are connected in tandem between a relatively fixed part 12 and a part 13 which may vibrate in directions parallel to the axes of the units 10, 11.

This vibration may be imparted by the unit 11, or from an external source. In the latter case oscillatory movement provided by the unit 11 is used to oppose and damp transmission of vibrations from the part 13 to the part 12. In the particular example the cylinder portion of the unit 10 is coupled to the part 12, and that of the unit 11 to the piston rod of the unit 10. The piston rod of the unit 11 is coupled to the part 13.

As shown in Figure 2 each of the units 10,11 is a double-acting unit having a cylinder 20 provided with passages 21,22 to which fluid pressure and return lines (not shown) may selectively be connected by operation of a known type of electrohydraulic valve 23. A piston 24 is slidable in the cylinder 20. In the present example the total stroke of the piston 24 is approximately 14 mm. It can be arranged that, by any known means, the piston 24 is locked relative to the cylinder 20 in the event of a hydraulic failure. A linear variable displacement transducer 28 is connected between the cylinder 20 and piston 24to provide an output signal indicative of the relative position of these elements.

As shown in Figure 1 control circuits 30,31 are responsive to electrical signals to provide control currents on lines 32,33 to the units 10, 11 respectively. The circuit 30 is responsive to a signal on a line 34 indicative of a required operating position of the unit 10, current being applied on the line 32 until a signal on a line 35 from the transducer in the unit 10 indicates that the desired position has been reached. In the absence of signals on the lines 36 and 37, the unit 10 may be used to position the part 13 relative to the part 12.

The circuit 31 is responsive to 27 Hz sine wave signals on a line 36, and also to further signals on a line 37, these further signals preferably also being in the form of a sine wave having a frequency which is considerably less than that of the signal on line 36.

The signals on lines 36,37 are combined in the circuit 31 to provide, on the line 33, a control current signal in which a 27 Hz frequency of small amplitude is superimposed on a lower frequency of considerably greater amplitude. The signal on line 33 will cause the unit 11 to provide an oscillatory output whose magnitude is typically 1 mm, the midpoint of that output continuously moving over a range of, for example, 4 mm, the frequency of this movement being of the order of 0.02 Hz. The signal on line 37 is also applied to the circuit 30 in a subtractive manner, so that in the absence of a signal on line 34 the unit 10 is operated at a frequency and magnitude equal to that of the lower frequency applied to the unit 11, and in the opposite sense thereto.Shifting of the operating midpoint of the unit 11 will not, therefore, affect the position of the part 13, relative to the part 12, selected by the signal on line 34.

Figure 3 shows a system according to the invention applied to higher harmenic control for reducing vibration induced in a helicopter body 40 by rotation of its blades 41. Figure 3 shows one such system only as applied, for example, to the collective pitch control of the blades 41, for which purpose the units 10,11 are coupled in tandem between a fixed part 12 in the body 40 of a helicopter and a cyclic pitch control rod for the blades 41 of the helicopter an identical arrangement of units 10, 11 will similarly be connected for control of the cyclic pitch of the blades 41. A pilots control 42 supplies signals to a computer 43 which generates signals on a line 44 indicative of the amount of collective pitch required. The computer 43 also generates signals on a line 45 to control cyclic pitch.The signals on line 44 are applied to a circuit 46, corresponding to the circuit 30 in Figure 1, which supplies current control signals to the unit 10.

A sensing device 47 in the helicopter body 40 may comprise a plurality of accelerometers and provide signals on lines 48 to a further computer 49. The computer 49 generates, on a line 50, signals indicative of the amount of oscillatory movement required from the unit 11 to oppose and effectively damp out vibrations which would otherwise be transmitted from the blades 41 to the body 40. The computer 49 also provides, on a line 51 corresponding signals indicative of the oscillating output required of a unit 11 in the cyclic control. The signals on line 50 are applied to a control circuit 52 which includes means for generating the low frequency, high amplitude signals which will cause the centre point of the oscillating movement of the unit 11 to be continually shifted. This signal is superimposed on the signal on line 50 and applied to the unit 11 as described above. The low frequency signal is also applied on a line 53 to the circuit 46 to cause the unit 10 to oscillate at the same frequency and magnitude, but in the opposite sense, as the lowfrequencyshiftofthe unit 11.

Claims

1. An actuator system comprising first and second actuator units connected in tandem, a first control means for causing said first actuator unit to provide an output which comprises a first oscillatory movement of a predetermined frequency and amplitude and a second oscillatory movement superimposed on said first movement, the frequency and amplitude of said second movement being respectively higher and less than those of said first movement, and a second control means for causing said second unit to provide a third oscillatory movement whose frequency and amplitude are substantially equal to those of said first movement, said third movement being opposite in sense to said first movement.

2. A system in which said control means comprises a device for generating first signals corresponding to a vibration transmitted to a relatively fixed part on which said actuator system is mounted, a first control circuit responsive to said first signals for generating second signals corresponding to the frequency and amplitude of said second oscillatory movement which is required to damp transmission of said vibration, said first control circuit generating signals of a predetermined frequency and amplitude corresponding to said first oscillatory movement, and in which said second control means comprises a device for generating a fourth signal corresponding to a desired position of said second actuator unit, and a second control circuit responsive to said third and fourth signals.

3. An actuator system substantially as hereinbefore described with reference to Figures 1 and 2 or Figure 3 of the accompanying drawings.